1. Field of the Invention
The present invention relates to a mercury wetted contact switch (hereinafter referred to simply as "mercury switch") and, more particularly, to a position-insensitive murcury switch.
2. Description of the Prior Art
In mercury swtich whose contact resistance is stabilized, chattering is prevented. The useful life of the switch is extended by forming a lasting film of conductive fluid (mercury) on the contacting part of each of the movable contact member and the fixed contact member, both of which are sealed in a container. This type of switch is used in various fields of many industry. If a switch has a large quantity of mercury sealed in its housing, to be supplied to the contacting parts, it is prevented from the normal operation by the movements of the pool of mercury unless its attitude of use is properly restricted. As a result, the switch tends to have limited applications. For this reason, a position-insensitive mercury switch is one for enabling a normal operation in any attitude, by appropriately limiting the quantity of mercury thereof.
A position-insensitive mercury switch, known in the prior art will be described below with reference to FIG. 1. A fixed side electrode 11 is positioned at one end of a sealed housing 13. An armature 12a of a movable side electrode 12 is positioned at the other end of the housing 13, these two electrodes being opposite each other in this housing 13. The armature 12a is connected to a stem 12c by way of a hinge spring 12b. The surface of the stem 12c within the housing 13, the armature 12a, the spring 12b and a fixed electric contact 11b positioned on a magnetic pole section 11a of the electrode 11 are all wetted with mercury. Meanwhile, the pole section 11a is treated so that it is not wetted with the mercury. The quantity of the mercury is controlled in advance so that the fixed contact 11b and the armature 12a are not short-circuited by the mercury, in any attitude of the mercury switch. Thus, there is no mercury pool which is present in a mercury switch whose attitude of use is specifically restricted.
In response to the impression of a magnetic field from outside bulb 13, a magnetic attractive force is generated between the electrode 11 and the armature 12a, each consisting of a magnetic substance. A result is that the flexibility of the spring 12b inclines the armature 12a to bring it into contact with the contact 11b, and between the fixed side electrode 11 and the movable side of electrode 12 which are thereby electrically connected to each other.
When the external magnetic field is removed, the armature 12a is restored to its usual position by the retractive force of the spring 12b. The electrodes 11 and 12 are then electrically isolated from each other.
Since the armature 12a and the contact 11b are wetted with the mercury, the contact between the contact 11b and the armature 12a is stabilized. Even if a spark occurs between them, the contact 11b and the armature 12a will be protected and their service lives will be prolonged. A method to manufacture such a position-insensitive mercury switch using a limited quantity of mercury is disclosed in the U.S. Pat. No. 3,116,384.
In such a mercury switch, however, the impact the armature 12a suffers from its collision with the contact 11b when the switch is turned on. The centrifugal force generated by the vibration of the armature 12a, when it is turned off, cause the mercury on the armature 12a to splash and adhere to the inner wall of the sealed housing 13. As a consequence, a problem arises, since the quantity of the mercury in the position-insensitive mercury switch, as described above, is limited to be no more than sufficient to wet the surface of the armature 12a. The contact face will become exposed after a repeated splashing of the mercury, to invite a considerable shortening of the useful life of the contact.